<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <script>
        //int num;
        //只是声明变量，，但是没有赋值，现在的值是undefined
        var v;
        console.log(v);//undefined
        console.log(typeof(v));//undefined
        v = 3.14;
        console.log(v);//3.14
        console.log(typeof(v));//number
        v = 'js';
        console.log(v);//js
        console.log(typeof(v));//string
        v = true;
        console.log(v);//true
        console.log(typeof(v));//boolean
        v = null;
        console.log(v);//null
        console.log(typeof(v));//object

        var m = '3';
        var n = 3;
        if (m == n) {//值相等就可以
            console.log('m==n');
        }
        if (m === n) {//值相等，类型也要相等
            console.log('m===n');
        }

    </script>
</body>
</html>